Aquatic Toxicology 30 (1994) 117-135 ; Interactions between copper and cadmium during single and combined exposure in juvenile tilapia O r e o c h r o m i s m o s s a m b i c u s :Influence of feeding condition on whole body metal accumulation and the effect of the metals on tissue water and ion content AbstractJuvenile tilapia (Oreochromis mossamhicus) were exposed for 96 h to ranges of sublethal concentrations of Cu or Cd, under both fed and non-fed conditions. Exposure to one metal (Cu or Cd) not only resulted in an increased whole body content of the metal exposed to, but also influenced the concentration of the other metal present in the fish. Furthermore, the total amount of Cu and Cd accumulated during exposure to heavy metals was influenced by the nutritional state of the fish. Besides exposure to either Cu or Cd, fish were also exposed to mixtures of Cu and Cd. Results indicated that accumulation during Cu/Cd co-exposure cannot be predicted by simple addition of the effects of single metal exposures. Obviously, complex interaction mechanisms are involved, as was concluded e.g. from the significantly decreased whole body Cd-content of Cu/Cd-co-exposed fish compared to the Cd-content of Cd-exposed fish. This phenomenon was observed in both fed and non-fed fish. Because ionic homeostasis is known to be affected by heavy metals, in this study also whole body water, calcium and sodium content in Cu and/or Cd-exposed fish were determined. The results indicate that also with respect to these parameters the two metals interact. The effects on water and ion appear to be dissociated. The data reveal previously unrecognized effects of interaction of the metals on whole body metal content, water and ion regulation.

Large parts of the floodplains in the Dutch Rhine basin can be considered wetlands of international importance. Few data are available concerning the threats to these wetlands. Legal protection and the principle of ' wise use' of the wetlands, as stipulated in the Ramsar Convention, are hardly being implementated in national and local policies. Until 1993 none of the floodplains in the river basin has actually been designated as wetland of international importance. In zoning plans the ' wetland function' is hardly ever recognized as the main function. A relatively small part of the river floodplains is designated as nature reserves or protected areas. More research should be carried out concerning the environmental quality of and ecological standards for wetlands. The physical threats of deterioration, disturbance and fragmentation of habitats deserve special attention. Legal protection and 'wise use' of wetlands in the Rhine basin should be further implemented.